Sagging Nacelles - HobbyTalk
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post #1 of 23 (permalink) Old 04-11-2007, 01:35 PM Thread Starter
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Sagging Nacelles

Anyone got a problem yet with the issue of the Big Refit's nacelles sagging?
Mine's has been built and decaled up so far and I have no problems. I'll try to post pics of my refit so you guys can see my job.
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post #2 of 23 (permalink) Old 04-11-2007, 01:52 PM
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I know of several folks who've mentioned the fact that they did not build their PL Refit w/an interior armature and have zero sagging on their pylon/nacelle assembly. Several of those had lit their models, as well. In fact, I don't know of anyone who's complained of sagging on their PL Refit thus far.

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post #3 of 23 (permalink) Old 04-11-2007, 01:57 PM
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I don't think they will sag. The supporting structure is much stronger and the nacelles are supported more in the middle than towards the front like the TOS E is.


Should be fine.
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post #4 of 23 (permalink) Old 04-11-2007, 02:30 PM
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It's plastic, while they don't seem heavy they do pose a load and will sage. About the only way around it is to build up a structure beneath it. Cult sells a structural integrety device, basically a metal frame designed to be used with the PL kit. Doing this or designing your own is about your only hope.... That or filling the nacelles with helium....
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post #5 of 23 (permalink) Old 04-11-2007, 03:16 PM
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Interesting that you say it's destined to "sage", John. I've built up more than half a dozen of the old ERTL Refit kits and not a one of them ever showed a sign of sag.

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post #6 of 23 (permalink) Old 04-11-2007, 03:21 PM
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no sag here

I have 2 one since late 2006 and my most recent (last week) and both are fine...loving'em

Last edited by 1711rob; 04-11-2007 at 03:21 PM. Reason: typo
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post #7 of 23 (permalink) Old 04-11-2007, 03:30 PM
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If you look at the pics, even the studio model's sagged a bit. I don't think they are supposed to be exactly straight up and down looking at them from the front of the ship over the suacer.
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post #8 of 23 (permalink) Old 04-11-2007, 03:32 PM
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What, are they supposed to have curved inward or something...?

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post #9 of 23 (permalink) Old 04-11-2007, 03:36 PM
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I've built 3 and had a sagging issue with one of them, but not due to the weight. During assembly I had to pull the secondary hull apart and the mounting bosses for the pylons took a bit of a beating and thats whats causing the sag.
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post #10 of 23 (permalink) Old 04-11-2007, 03:46 PM
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I don't mean to burst anyone's bubble, but given enough time those engine supports will begin to sag. How much time? Beats me; how long did it take the the Unobtanium miniature's supports to start sagging?

It's a question of gravity. Anyone who builds this gravity-challenged model without taking an extra measure of care to ensure against the inevitable onslaught of nacelle droop is asking for trouble.
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post #11 of 23 (permalink) Old 04-11-2007, 03:48 PM
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Quote:
Originally Posted by rossjr
It's plastic, while they don't seem heavy they do pose a load and will sage. About the only way around it is to build up a structure beneath it. Cult sells a structural integrety device, basically a metal frame designed to be used with the PL kit. Doing this or designing your own is about your only hope.... That or filling the nacelles with helium....
I agree....It's wise to simply put in a supporting structure to guarantee over time it won't sag.....In my Ertl enterprises, all I had to do was to glue in a L shaped piece of bent coathanger wire using white glue. No sag here.

Last edited by Old_McDonald; 04-11-2007 at 03:49 PM.
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post #12 of 23 (permalink) Old 04-11-2007, 04:22 PM
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And I'll maintain, once again, that out of all the ERTL Refits I built I never once reinforced the pylons and never had one sag. I've got one that's been built up for nearly a decade now and it's still at the correct angle from the day I put it there. The only thing I did differently than most folks is that I used CA instead of standard "welding" glues that tend to melt the styrene to form a new bond. CA doesn't melt the plastic.

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post #13 of 23 (permalink) Old 04-11-2007, 05:52 PM
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Regarding PL refit sag, where would the weak points be?

The struts?
The nacelle struts themselves aren't likely to deform, as their cross-section is hollow, with a higher moment of inertia (IMHO) than the Ertl solid struts. Also, they won't shear along the seams if glued properly. So they're solid.

Where the strut meets the nacelle?
The joint at the top of the strut doesn't experience much (axial?) torque, since it's located close to the centerline of the nacelle. So it's not likely to contribute to sag.

Will the secondary hull deform under the torque?
Maybe the secondary hull will deform inward slightly along the, er, "waterline", but then again it may not, as the shuttlebay assembly should provide support there. If not, I'll place some support between the hull and the shuttlebay. I don't think the sec hull would deform at the dorsal spine either, since the torque would pull on either side of the spine, and the top piece of the sec hull is one piece, not two like the Ertl. (If it were two pieces, we'd have a load on the center seam there.) So I don't think the secondary hull will deform. I also don't think the dorsal piece would deflect upward but I might add something inside the hull to connect the dorsal spine to the shuttlebay ceiling and/or walls for reinforcement.

How about the bottom end of the strut?
So we're left with the joint where the strut meets the secondary hull to cause deflection and sag. No surprise. Yep, there's torque here, but I think that because of the push/pull two-joint design of the internal connection, the load is actually transferred to the secondary hull pieces, sort of like a monocoque. If the sec hull pieces are glued properly, I can't see them shearing along the joint, and as I wrote, I can't see the hull deforming either.

Now an armature certainly couldn't hurt, but I wouldn't assume that these things will sag. The design is different from the Ertl design, transferring the load in some clever ways.

Now all this is just idle speculation until an engineer gets a chance to publish an analysis of this thing. That would be interesting.
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post #14 of 23 (permalink) Old 04-11-2007, 06:02 PM
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Quote:
Originally Posted by SteveR
Regarding PL refit sag, where would the weak points be?

Now an armature certainly couldn't hurt, but I wouldn't assume that these things will sag. The design is different from the Ertl design, transferring the load in some clever ways.

Now all this is just idle speculation until an engineer gets a chance to publish an analysis of this thing. That would be interesting.
I didn't get the PL Refit. (no rocks please) as it's just too big for me. But I did notice that some of the styrene used over the years for the Ertl kits seem to change from issue to issue. Some styrenes were "softer" than others and these seemed to sag. Since the, I used the support without gambling on the quality of the styrene.
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post #15 of 23 (permalink) Old 04-11-2007, 06:11 PM
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Ah, you mentioned something I left out: the styrene itself. Since it's not dimensionally stable, it should contribute to sag, no?

But would it be noticeable?
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